The importance of fluid disinfection for providing a fluid that contains fewer harmful bacteria has widely been recognized. This becomes even more prescient when the fluid in question is, for example, water that is being prepared for human or animal consumption.
Fluid disinfection with UV radiation was first used in the 1980's; it has numerous advantages over other methods such as chlorination, especially when the fluid is water that is to be consumed. UV radiation does not affect the PH, composition, taste or odor of the fluid that has been disinfected. The disinfection of the fluid is achieved by deactivating the DNA of bacteria, viruses and microbes. Further advantages of the use of UV to disinfect fluids are simple installation, less maintenance requirements and space efficiency. Furthermore the use of UV to treat the fluid eliminates the need to use a chemical process thus removing the risk of a chemical smell or taste in the fluid after disinfection has been completed.
Current UV water disinfection technologies mainly use mercury discharge lamps to provide the UV radiation that disinfects the water. Generally these systems provide UV radiation to fluids flowing past them.
U.S. Pat. No. 7,520,978 discloses a system for purifying a fluid using ultra violet (UV) light to inactivate micro-organisms present in the fluid. The system has an arrangement of UV light emitters on perforated plates. The fluid, while passing through perforations in the perforated plates, is exposed to the UV light emitted by the UV light emitters. Micro-organisms present in the fluid pass very close to the UV light emitters. The UV light absorbed by the micro-organisms causes genetic damage and inactivation. The system has feedback units providing feedback about the physical properties of the fluid to a power unit supplying power to the UV light emitters. The power unit varies the amount of power supplied to the UV light emitters, based on the feedback.
Ultraviolet (UV) radiation disrupts the DNA of microbes and thereby prevents reproduction. Without reproduction, the microbes become far less of a danger to health. As such UV radiation is a mutagen, that is to say, UV radiation creates mutations within the structure of DNA. UV-C radiation in the short wavelength range of 100-280 nm acts on thymine, one of the four base nucleotides in DNA, when a UV photon is absorbed by a thymine molecule that is adjacent to another thymine within a DNA strand, a covalent bond or dimer between the molecules may be created, this is different to the normal structure of DNA wherein the bases always pair up with the same partner on the opposite strand of DNA. This causes a bulge to occur between the two bases, the bulge prevents enzymes from “reading” the DNA and copying it, thus neutering the microbe.
Some pathogens are hundreds of times less sensitive to UV radiation and the subsequent risk of mutations than others. Viruses may require a 10-30 times greater dose of UV light than Giardia or Cryptosporidium which are protozoa.